A device of three-chamber type for purifying wastewater is known through WO 00/04972. The device is a favorable alternative to an ordinary septic tank, which accomplishes a mechanical purification of wastewater supplied to it. Sludge and sediments are gathered on the bottom of the device and have to be removed at intervals.
Although the device is effective in its intended function, the demands on cleaning or purification are increasing, also on smaller plants intended for one or a few households.
In order to improve the purification, it may be necessary to go to chemical purification, where a flocculation agent or precipitation agent is added to the wastewater in a controlled way.
The main object of the invention is thus to modify the existing device so as to enable a chemical purification.